Showing papers in "Journal of Hydrologic Engineering in 2003"

Nonlinear model for drought forecasting based on a conjunction of wavelet transforms and neural networks

Abstract: Droughts are destructive climatic extreme events that may cause significant damage both in natural environments and in human lives. Drought forecasting plays an important role in the control and ma...

Comparative Analysis of Event-Based Rainfall-Runoff Modeling Techniques—Deterministic, Statistical, and Artificial Neural Networks

Abstract: Modeling of an event-based rainfall-runoff process has been of importance in hydrology. Historically, researchers have relied on conventional modeling techniques, either deterministic, which consid...

Nonparametric Approach for Estimating Return Periods of Droughts in Arid Regions

Abstract: Droughts cause severe damage in terms of both natural environments and human lives, and hydrologists and water resources managers are concerned with estimating the relative frequencies of these events. Univariate parametric methods for frequency analysis may not reveal significant relationships among drought characteristics. Alternatively, nonparametric methods provide local estimates of the univariate and multivariate density function by using weighted moving averages of the data in a small neighborhood around the point of estimation and opposed to parametric methods. A methodology for estimating the return period of droughts using a nonparametric kernel estimator is presented in order to examine the univariate as well as the bivariate behavior of droughts. After evaluating and validating a nonparametric kernel estimator, a drought frequency analysis is conducted to estimate the return periods of droughts for the Conchos River Basin in Mexico. The results show that, for the univariate analysis, the retur...

Radial Basis Function Neural Network for Modeling Rating Curves

Abstract: The establishment of a rating curve is an important problem in hydrology. Generally, a regression approach is applied to establish the relationship between stage and discharge. However, this approach fails in the cases where hysteresis is present in the data. The aim of the study is to investigate the potential of employing radial basis function (RBF) type neural networks for modeling stage-discharge relationships at gauging stations and to compare different types of networks. The results are promising and suggest that the neural network approach is highly viable. A comparison of the RBF models with backpropagation type neural networks reveals that the former is superior in performance for rating curves exhibiting hysteresis.

Artificial Neural Network Approach for Predicting Transient Water Levels in a Multilayered Groundwater System under Variable State, Pumping, and Climate Conditions

Abstract: The feasibility of training an artificial neural network (ANN) for accurately predicting transient water levels in a complex multilayered ground-water system under variable state, pumping, and climate conditions is demonstrated. Using real-world data, an ANN was developed for a public supply wellfield and ground-water monitoring network located near Tampa Bay, Florida. The ANN was trained to predict transient water levels at 12 monitoring well locations screened in different aquifers in response to changing pumping and climate conditions. The trained ANN was then validated with ten sequential seven-day periods, and the results were compared against both measured and numerically simulated ground-water levels. The absolute mean error between the ANN predicted and the measured water levels is 0.16 m, compared to the 0.85 m absolute mean error achieved with the calibrated numerical model at the same locations over the same time period. The ANN also more closely reproduced the dynamic water level responses to pumping and climate conditions. The practical implication is that if ANN technology can achieve superior ground-water level predictions, it can be used to improve management strategies for a wide range of ground-water problems, from water quantity to water quality issues. It can also serve as a powerful sensitivity analysis tool for quantifying interrelationships between different variables, fostering a better understanding of the hydrogeologic system, and improving future modeling endeavors. And while physical-based numerical modeling retains some advantages over the ANN technology, both approaches may be used in a complementary fashion to achieve sound decision-making for complicated ground-water management problems.

Bivariate Drought Recurrence Analysis Using Tree Ring Reconstructions

Abstract: Droughts may be represented by two main characteristics—duration and severity. In this paper, a general methodology to evaluate the frequency and risk of the occurrence of droughts is presented using a bivariate drought characterization. The theory of runs is applied to model drought recurrence as an alternating renewal process, describing droughts simultaneously in terms of their durations and severities. Short historical records usually do not allow reliable bivariate analyses. However, tree ring reconstructions of droughts provide information about past events, allowing the analysis. An approach to adapt and include dendrochronology reconstructions combined with historical records to characterize droughts is presented. The proposed approach uses the stochastic structure of the residuals of paleo reconstructions to generate equally likely representations of past drought events. The procedure was applied to paleo and historical records in Texas Climatic Division 5 and compared with univariate analyses. T...

Peak Discharge Scaling in Small Hortonian Watershed

Abstract: Runoff data were analyzed from the semihumid 21.2 km 2 Goodwin Creek Experimental Watershed ~GCEW! in northern Mississippi to examine watershed response over a range of scales. Runoff is monitored at the GCEW outlet and in 13 subcatchments, ranging in area from 0.06 to 17.6 km 2 . Previous data-based studies have shown that simple scaling theory fails to describe scaling of flood quantiles in large watersheds, and there is a fundamental change in scaling behavior in semihumid watersheds at an area of approximately 100 km 2 . It has been found that flood quantiles in nearly all subbasins in the GCEW are self-similar as described by simple scaling theory. It has also been found that expected values of peak flows during single runoff events are described by a power law function of catchment area. The primary reasons why flood quantiles are self-similar on Goodwin Creek are that precipitation is relatively uniform over the basin; peak discharges in smaller catchments are highly correlated with rainfall rates; nearly the entire watershed regularly contributes to runoff and; the groundwater table plays little role in runoff production.

Radar-Based Flood Warning System Applied to Tropical Storm Allison

Abstract: Flood warning systems in urban areas have greatly improved in recent years with the advent of geographical information systems (GIS), radar-based rainfall estimation using next generation radar (NEXRAD), and delivery systems on the internet. The issue of flood warning and alert was brought to the forefront of public attention in Houston, Texas after the devastation resulting from the Tropical Storm Allison flood of June, 2001. This flood was reported by the National Oceanic and Atmospheric Administration as the most damaging urban flood in U.S. history, and certainly the most devastating event to impact Houston and Harris County with over $5 billion in total damages, and about 50,000 damaged structures. Over $1.5 billion in damages to the Texas Medical Center (TMC) alone were reported, with additional major impacts to the local community. While more traditional gage-based alert systems often provide flood notification to many people, the combination of GIS, NEXRAD, and the internet allows for the more efficient accumulation of rainfall data in real-time. This data can then be used in hydrologic models to estimate peak flows in a basin. This paper will illustrate the design, operation, and performance of an advanced flood warning system, developed for the TMC, which utilizes NEXRAD radar for hydrologic prediction in the Brays Bayou watershed of Houston, Texas. It will specifically document and review its use during the T.S. Allison storm event and other historical events.

Simple, Practical Method for Determining Station Weights Using Thiessen Polygons and Isohyetal Maps

Abstract: A simple, practical method for computing station weights, which are commonly used in operational (i.e., real-time) hydrologic modeling, is presented. The weights are derived using Thiessen polygons and widely available isohyetal information. The method is shown to eliminate long-term bias associated with the difference between the spatial distribution of precipitation implied by Thiessen polygons and the more accurate spatial distribution depicted by an isohyetal map.

Nonlinear Hydrologic Processes: Conservation Equations for Determining Their Means and Probability Distributions

Abstract: The point-location-scale conservation equations of hydrologic processes, when viewed at the scale of computational grid areas, become stochastic partial differential equations (PDEs). For the upscaling of the point-location-scale conservation equations to the scale of computational grid areas, a common approach is to develop the ensemble averages of these equations. Accordingly, in this study general ensemble average conservation equations for determining the probabilistic and mean behavior of nonlinear and linear hydrologic processes are developed to exact second order. From the derived equations it is seen that the evolution equation for the probabilistic behavior of a generally nonlinear hydrologic system becomes a Fokker–Planck equation (FPE). As such, the determination of the probabilistic behavior of a hydrologic system of processes reduces to the solution of a linear, deterministic PDE, the FPE, under appropriate initial and boundary conditions. The solution of the FPE yields the probability density function of the hydrologic system which can then be used to obtain the means of the state variables of the system by the expectation operation. One can also determine the mean behavior of nonlinear stochastic hydrologic processes by means of master key ensemble average conservation equations developed in this study. Upon examination of these generic deterministic equations, one may note that they are implicit integro-differential nonlinear equations in the mixed Eulerian–Lagrangian form. Meanwhile, the master key equations which were developed also for linear hydrologic processes, are explicit, linear PDEs.

Flood Forecasts for Urban Basin with Integrated Hydro‐Meteorological Model

Abstract: We describe a system for forecasting flood risk in the 370 km2, largely urban Kifissos Basin, Athens, Greece, located in moderate to steep terrain (∼3 h hydrologic response time). A 42 h flood forecast lead time is achieved through the use of an integrated hydro-meteorological system. Rainfall is forecast, on a 6 km grid, with a chain of nested numerical weather prediction models, consisting of a limited area model initialized with results of a global circulation model. Flood risk is assessed by driving a hydrologic model with the forecasted rainfall. The system’s forecast skill is evaluated for two recent, medium-size storm events. Results are encouraging for this initial operational stage, however, they also indicate that integrated hydro-meterological models are not yet mature tools. The weaker part of flood risk assessment is the rainfall forecast, which underestimated cumulative depths and maximum intensities and overestimated duration.

Unsteady Stream Depletion when Pumping from Semiconfined Aquifer

Abstract: A solution is obtained for flow depleted from a stream when water is pumped from an adjacent well in a semiconfined aquifer. The streambed partially penetrates the aquitard, which forms the top boundary of the pumped aquifer, and the distance between the well and stream is assumed large enough to allow the stream to be modeled with a zero width. The governing partial differential equations for this problem are shown to be equivalent to the equation postulated and solved by Boulton for flow to a well in a delayed-yield aquifer. Consequently, drawdown curves and plots of stream depletion versus time are all found to have two inflection points. However, unlike the solution behavior for Boulton’s problem, aquifer recharge furnished by the stream causes all drawdown and stream depletion curves to approach horizontal asymptotes as time becomes infinite. The solution calculated herein is general enough to reduce to a solution calculated earlier by Hunt when the aquitard becomes impermeable.

Simple Estimation of Prevalence of Hortonian Flow in New York City Watersheds

Abstract: This study was a statistical evaluation of the prevalence of infiltration excess runoff ~i.e., Hortonian flow ! for undeveloped areas within New York City ~NYC! watersheds. Identifying the hydrological processes generating runoff is central to developing water- shed management strategies for protecting water quality. Fifteen-minute rainfall data from East Sidney, N.Y. ~1971-2002! were used as maximum observed intensities. Maximum exceedance analyses were performed on a monthly basis to investigate seasonal rainfall intensity trends. Hortonian flow was assumed to occur whenever the rainfall intensity exceeded the soil permeability. Soil permeabilities were obtained from the U.S. Natural Resource Conservation Service soil survey. Results show that Hortonian flow is unlikely to occur anywhere for events smaller than the 3-year 15-min event. Only for the summer months, May-August, is Hortonian flow expected for 15-min intensities of ,10-year magnitude. However, the summer results are overpredicted by this analysis because these months typically have the driest soil conditions and thus the highest infiltration capacity. This analysis concludes that infiltration excess runoff is not a dominant runoff process in undeveloped portions of NYC watersheds.

Simplified Two-Parameter Gamma Distribution for Derivation of Synthetic Unit Hydrograph

Abstract: Several methods for synthetic unit hydrographs are available in the literature. Most of them involve manual, subjective fitting of a hydrograph through few data points. Because it is difficult, the...

Estimating Instantaneous Peak Flow from Mean Daily Flow Data

Abstract: Estimation of the design flood flow for hydraulic structures is often performed adjusting probabilistic models to daily mean flow series. This may cause an underdesign of the structure capacity with possible risks of failure, because instantaneous peak flows may be considerably larger than daily averages. Estimation of the instantaneous peak flows is often needed for simulation of the reservoir operation based on the hydraulic characteristics of the structures and the operation rules. Because there is often a lack of instantaneous flow data at a given site of interest, the peak flow has to be estimated. This paper develops a new method to estimate the instantaneous peak flow from mean daily flow data. This methodology was successfully applied to a series of flow information from gauging stations in Brazil, with important improvements compared to the traditional methods available in the literature.

Ecology Ditch: A Best Management Practice for Storm Water Runoff Mitigation

Abstract: A full-scale physical model of a modified infiltration trench was constructed to test a new storm water best management practice called an ecology ditch. The ditch was constructed using compost, sand, and gravel, and a perforated drain pipe. A series of 14 tests were conducted on the physical model. The tests controlled rainfall application and overland roadway runoff amounts and monitored outflow from the discharge pipe. The objectives were to increase the time to peak and reduce the peak discharge coming out of the pipe. The results were also used to calibrate a modified existing unsaturated two-dimensional groundwater flow code. After the code was calibrated, computer simulations were performed to determine the effects of storm size, rainfall distribution, constant rainfall application, media type, initial conditions, and the physical size of the ecology ditch. The simulations used 24-hour duration storm sizes of 0.64, 1.27, 2.54, 3.81, 5.08, and 6.35 cm (0.25 to 2.5 in.). Peak reduction was found to d...

Entropy-Based Parameter Estimation for Kappa Distribution

Abstract: Proposed in this study is an approach to estimate regional evapotranspiration from potential evaporation using a distributed hydrologic model. If water is freely available in the storage tank of interest, evapotranspiration is taken as Penman’s potential evaporation. Otherwise, the reduction of actual evapotranspiration from potential evaporation is estimated using the simplified Philip’s soil-moisture relationship with the combination of a physically based distributed tank (PDTank) model. The average annual evapotranspiration in the study area is estimated to be 716 mm. Results are also compared with the actual evapotranspiration estimated by using Morton’s complementary relationship areal evapotranspiration (CRAE) model and Brusaert-Stricker’s advection-aridity (AA) model. These three models give quite similar performance of goodness. The AA model gives the largest estimation for the annual evapotranspiration, the physically based distributed tank (PDTank) model gives the smallest estimation, and the CRAE model shows the amount in-between the AA model and the PDTank result. But the PDTank gives better results than both the CRAE and the AA models for winter evapotranspiration.

Sampling Adjustment Factors for Rainfall Recorded at Fixed Time Intervals

Abstract: Precipitation data collected at fixed time intervals will most likely miss true maximum accumulations for durations equal or close to the sampling interval. This becomes a problem when fixed-interval rainfall data are used for frequency analysis. Sampling adjustment factors (SAF) are often used to correct for this mismatch between true and observed maxima. An SAF is the average ratio of the true maximum accumulation to the maximum given by a fixed-interval gauge record. This paper uses high temporal-resolution data from ALERT-type rain gauges in the Kansas City area to derive an empirical relationship for SAF versus the sampling ratio, which is the ratio of the duration of interest to the sampling interval. This relationship is consistent across durations ranging from 1 to 24 h, and is in good agreement with other studies.

Autorun Persistence of Hydrologic Design

Abstract: Persistence is the most important property in any hydrologic design concerning the storage capacity of reservoirs, average return periods, failure risks, and drought properties. Its consideration in analytical derivations of design criteria presents difficulties, especially in autocorrelated hydrologic processes, and for this reason, most often the analytical expressions are obtained on the basis of non-persistent (independent) cases. Although the conventional autocorrelation coefficients and function are used in many hydrological design problems, the very definition of the autocorrelation function requires that the underlying hydrologic process generating mechanism abide with normal (Gaussian) probability distribution function in addition to other restrictive assumptions. Since almost all of the analytical stochastic approaches are based on the normality assumption, it is necessary to transform non-Gaussian distributions to the normal distribution to use analytical expressions. During the transformation ...

Numerical Modeling of Saline Intrusion in Salar de Atacama

Abstract: This paper presents the results of numerical simulations of groundwater circulation and solute transport at the Salar de Atacama through use of a numerical model to solve the two-dimensional problem of flow in an aquifer when considering the effects of variable density. The phenomena associated with solute transport are modeled by means of an advection-dispersion equation, and a linear relationship is assumed between fluid density and concentration of the dissolved solids. Simulations considered conditions of high groundwater evaporation, which depends on the depth of the phreatic surface. Results indicate that the discharge of groundwater occurs essentially in freshwater-saline water interface zones, where a number of lagunas begin. Different freshwater recharge scenarios were simulated, while it was verified that the effects of evaporation are important and minimize or buffer the variations in the phreatic surface and the discharges of groundwater that are the source of water supply for the lagunas.

Hydrologic Behavior of Residual Soil Slopes in Singapore

Abstract: Monitoring hydrologic responses of slopes is critical for advancing hillslope hydrologic studies. Storm- and time-based continuous hydrologic responses from three instrumented hillslopes in Singapore were monitored for a period of 420 days to observe the impact of rainfall on the pore-water pressure changes and runoff generation. Analyses of the hydrologic data indicate that only about 37% of the annual rainfall events are capable of producing runoff, and a threshold rainfall of about 10 mm is required to produce runoff. The seasonal distribution of pore-water pressures showed that the slopes experience high matric suctions during dry periods that are compa- rable to matric suctions observed in other tropical climates, and positive pore-water pressures during wet periods, that are higher than in other geographic locations. A high correlation between the increase in pore-water pressure and the daily rainfall may provide a convenient estimate of the increase in pore-water pressure due to the daily rainfall. The variability of hillslope hydrologic responses from storm to storm is distinctive when compared with previous results at other geographic locations.

Effects of aquifer anisotropy on the migration of infiltrated stream water to a pumping well

Abstract: Pumping of groundwater near a stream can induce infiltration of stream water into the surrounding aquifers. Analysis of the migration of the infiltrated stream water to the pumping well is importan...

Improved Decomposition Solution to Green and Ampt Equation

Abstract: Here, the author expands on the results of the paper “Explicit Solution to Green and Ampt Infiltration Equation” by Serrano published in 2001. Specifically, new simple expressions are given for the cumulative infiltration depth and the infiltration rate that include more terms in the decomposition series. These expressions improve the results and overcome the transcription errors in Eqs. (16) and (17) in the paper by Serrano. A criterion for the convergence of the series is given with graphical illustrations of applications. Generally, the decomposition solution is accurate for a wide range of soil and hydrologic parameters. Important errors occur when the rainfall rate is very high relative to the soil hydraulic conductivity (e.g., high rainfall intensity on clayey soils). As time increases, the errors decrease and the decomposition solution is accurate.

Joint Seasonal/Annual Flood Frequency Analysis

Abstract: Flood frequency analysis, as commonly practiced, focuses on the estimation of return periods associated with annual maximum flood peaks of various magnitudes. In some applications, it is desirable to perform joint (i.e., simultaneous) flood frequency analyses on seasonal as well as annual bases. However, a problem one encounters in seasonal flood frequency analysis is that the consistency or interrelationship that must exist between the annual maximum and individual seasonal flood frequency distributions may not be preserved. The most important cause of inconsistencies is that one cannot arbitrarily specify the parametric forms of the annual and all of the seasonal distributions. A correct theoretical analysis of the joint frequency problem would require the use of a rather unusual and complicated distributional model. Since this is not practical, this paper presents two approximate but useful methods for joint frequency analysis using the log Pearson Type 3 distribution. It is shown via examples that the two methods can be applied to reasonably model annual and five seasonal flood distributions in the Tennessee Valley.

Probabilistic Solution to Stochastic Overland Flow Equation

Abstract: The point-location-scale conservation equations of hydrologic processes, when viewed at the scale of computational grid areas, become stochastic partial differential equations (PDEs). For the upscaling of the point-location-scale conservation equations to the scale of computational grid areas, a common approach is to develop the ensemble averages of these equations. Accordingly, in this study general ensemble average conservation equations for determining the probabilistic and mean behavior of nonlinear and linear hydrologic processes are developed to exact second order. From the derived equations it is seen that the evolution equation for the probabilistic behavior of a generally nonlinear hydrologic system becomes a FokkerPlanck equation (FPE). As such, the determination of the probabilistic behavior of a hydrologic system of processes reduces to the solution of a linear, deterministic PDE, the FPE, under appropriate initial and boundary conditions. The solution of the FPE yields the probability density function of the hydrologic system which can then be used to obtain the means of the state variables of the system by the expectation operation. One can also determine the mean behavior of nonlinear stochastic hydrologic processes by means of master key ensemble average conservation equations developed in this study. Upon examination of these generic deterministic equations, one may note that they are implicit integro-differential nonlinear equations in the mixed EulerianLagrangian form. Meanwhile, the master key equations which were developed also for linear hydrologic processes, are explicit, linear PDEs.

Weighted-Climate Parametric Hydrologic Forecasting

Abstract: This paper briefly summarizes an existing nonparametric method for using meteorology probability forecasts in operational hydrology and extends it for parametric estimation. The methodology builds a sample of possibilities for the future, of climate series from the historical record, which is weighted to agree with selected forecasts of meteorology probabilities. The nonparametric method concentrates on isolated event probabilities rather than on the entire probability distribution for various variables. It sometimes assigns the same weight to all climate series in selected categories, resulting in the same relative frequency for those climate series. By changing to a parametric approach, one determines entire probability distributions that match available forecast meteorology probabilities. This allows a continuous distribution of probability across a variable, not always possible with the nonparametric approach. This paper illustrates both the nonparametric and the parametric methods with an example, comments on both approaches, and evaluates both in a selected comparison.

Estimation of Aquifer Diffusivity from Stream Stage Variation

Abstract: A computationally simple method for the estimation of aquifer hydraulic diffusivity from observed piezometric-head variation because of an arbitrary variation in stream stage is proposed. The method makes use of the Fourier series representation of the arbitrary stream-stage variation. The piezometric-head variation due to a sinusoidal change in stream stage is derived in a computationally simple form, which was used as a basic solution in the method. Application of the method on a published data set shows that it accurately estimates the aquifer hydraulic diffusivity with less computational effort and can take into account any variation in stream stage.

Hydrologic Impacts of Disturbed Lands Treated with Dust Suppressants

Abstract: This study presents research on changes in hydrologic characteristics of disturbed land surfaces that have been treated with dust suppressants. Disturbed land surfaces, such as construction sites and unpaved roads, are sources of fine particulate matter. The application of dust suppressants affects the runoff characteristics as well as the water quality of the runoff. The changes in runoff characteristics were investigated in the field using a rainfall simulator on plots treated with 11 different dust suppressants. The rainfall simulation system was able to provide a uniform distribution of rainfall over a 2.4×2.4 m (approximately) plot at relatively low rainfall intensities (21 mm/h). Results of the study indicate changes in runoff rates and volume, and the timing of runoff initiation. The majority of the plots had higher runoff volumes and an earlier time of runoff initiation as compared to the control plot. The total suspended solids in the runoff were reduced for the majority of the plots. Extrapolati...

Modeling Event-Based Temporal Variability of Flow Resistance Coefficient

Abstract: During the storm duration, the effects of surface resistance on the developing and receding overland flow depths (hj) on different flow parameters like the overland flow resistance coefficient (Nj), flow velocities (vj), Reynolds number (Rj), and Froude number (Fj) have been studied for the six natural catchments (0.012–92.5 km2) located in different agroclimatic regions of India. The kinematic wave (KW) equations are used for simulation of overland and channel flows using explicit methods for developing numerical solutions for the estimation of flow parameters at short durations. For the complete storm duration hj-Nj relationships have been found to form hysteresis loops. To predict resistance coefficients, simple hj-Nj relationships have been worked out separately for the rising and depleting overland flow conditions. Computed hydrographs simulated by incorporating these equations in the KW model agree well with the observed ones. The overall applicability of the suggested approach is successfully demon...

Estimating Basin Evapotranspiration Using Distributed Hydrologic Model

Abstract: Runoff data were analyzed from the semihumid 21.2 km² Goodwin Creek Experimental Watershed (GCEW) in northern Mississippi to examine watershed response over a range of scales. Runoff is monitored at the GCEW outlet and in 13 subcatchments, ranging in area from 0.06 to 17.6 km². Previous data-based studies have shown that simple scaling theory fails to describe scaling of flood quantiles in large watersheds, and there is a fundamental change in scaling behavior in semihumid watersheds at an area of approximately 100 km². It has been found that flood quantiles in nearly all subbasins in the GCEW are self-similar as described by simple scaling theory. It has also been found that expected values of peak flows during single runoff events are described by a power law function of catchment area. The primary reasons why flood quantiles are self-similar on Goodwin Creek are that precipitation is relatively uniform over the basin; peak discharges in smaller catchments are highly correlated with rainfall rates; nearly the entire watershed regularly contributes to runoff and; the groundwater table plays little role in runoff production.